In the oil and gas industry, rock samples are routinely collected and analyzed for determining geophysical properties downhole. Historically, those skilled in the art have only looked at features inherently present on the surface of rock samples for referencing specific sites to be analyzed. The inherent features are used to reference each point/location on the samples. Although this process of locating features on the surface of the rock samples using an optical inspection of the features of the rock sample itself may be repeatable, this process is greatly undesired because of the amount time involved in having to re-align the exact location of the specific site to be analyzed.
As can be imagined, there are other issues that can arise from having to re-align the specific site for analysis by using only optical inspection, especially after a rock sample has been removed from a tester and later reinserted. Further, some rock samples are heated during the testing process. Heating the samples may sometimes change the topography of the samples, making it almost impossible to optically locate and re-align the specific site to be analyzed.
Locating microscopic features on a surface has been needed in other fields, such as semiconductor fabrication. For example, it is known in the art of semiconductor fabrication to induce a top passivation layer of a semiconductor chip with alignment marks for forming induced topographical features that are used for more easily locating selective areas of the chip. For example, FIG. 1 illustrates a semiconductor chip 100 having alignment markers 10 according to the prior art. As shown in the illustration, the alignment markers 10 have been formed so that each mark 10 is aligned with a particular edge of the chip 20.
The purpose for inducing these alignment markers 10 on the semiconductor chip 100 is so that the chip 100 may be more readily aligned for analysis and testing. In other words, by using the alignment markers 10, the chip 100 may be quickly and accurately positioned for testing. As shown, the alignment markers 10 also include a rectangular or square portion 15 near each mark 10. These portions 15 serve to indicate which quadrant the chip 100 lies (i.e., the chip's directional orientation). Alignment markers 10 related to semiconductor chips are detailed in U.S. Pat. No. 6,975,040, which is incorporated herein in its entirety.
Semiconductor chips normally have a planned mapping of recognizable properties, making it conducive to finding features of interest on the chip. For example, when finding features of semiconductor chips, there are still some distinguishable areas of the chip that can be identified (e.g., known metal areas on the chip, through which bonding pads may provide electrical contact with other conductive surfaces). Furthermore, any markings on semiconductor chips are produced during the fabrication process. These prefabricated marking then allow the chip to be aligned later for analysis based on mapped information in a database for the chip.
On the other hand, rock samples are completely unmapped, having an utterly random surface and a complete natural distribution of topographical features. Thus, rock samples are typically completely indistinguishable. For this reason, existing visual distinctions have always been used in locating regions of interest on rock samples.
Because the current method of locating and re-aligning specific sites on rock samples by optically inspecting inherent features of the rock samples is inefficient and can cause inconsistencies during sample analysis, and because rock samples do not undergo a fabrication process where alignment markers can be introduced, it is desirable to have a process for introducing marks on a rock sample for quickly and repeatedly establishing the exact location of the specific site to be analyzed. The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.